Sigourney Weaver’s face isn’t the first one you see in Ridley Scott’s “Alien” — she’s not even the first name you see, popping up second in the opening credits to Tom Skerritt — but there’s no question that Scott’s 1979 sci-fi masterpiece is a film (and, now, an entire franchise) that lives and dies based on the strength of Weaver’s indelible Ellen Ripley. She doesn’t even begin to emerge as the film’s principal hero until about 45 minutes in, when Ripley steps up in the wake of the kind of calamitous tragedy that still makes the film such a heart-pounding to watch, nearly four decades on.

Scott’s choice to ultimately center his film around the strength of a female character was hardly the kind of thing that other late-’70s action-driven blockbusters dug into (screenwriter Dan O’Bannon first wrote Ripley as a male lead, Scott was the one who hit upon the idea to change the character’s gender). While 1979 marked a sea change at the box office — the top earner was “Kramer vs. Kramer,” of all things — other big budget offerings that made off that same year were mostly male-driven, including “Apocalypse Now,” “Rocky III,” and “Moonraker.” The year before, films like “Superman,” “National Lampoon’s Animal House,” and “Jaws 2” also did brisk business at the box office. The “Star Wars” franchise was beginning to take shape, and production began on “The Empire Strikes Back” just two months before “Alien” landed in theaters.

A female badass like Ripley was something new, something bold, and Weaver and Scott made good on the promise of such a character — and she’s still one of the most memorable and enduring heroines ever.

When we first meet Ripley, she’s just as petty and aggrieved as the rest of the just-awakened Nostromo crew. Scott takes his time letting on what the real star of the film is, and you’d be correct to spend the first hour or so of “Alien” thinking that it’s Skerritt, who stars as Captain Dallas. But as the rest of the crew is winnowed away by one hell of a murderous alien creature, Ripley becomes a de facto leader who is forced into a heroic position that she soon discovers suits her just fine.

In early moments, Ripley reads as starkly human. She’s curious and brash and outspoken, unafraid of voicing her opinion to either Dallas or Ash (Ian Holm) in the midst of the facehugger freakshow that has set the Nostromo alight. Ripley evolves quickly, however, moving from unformed ideas (“Well, good! Let’s get rid of it!” is certainly a good way to deal with an alien force bent on killing you, though it lacks actionable items) and a deference to Dallas, straight on to steel-jawed determination and a brand new plan (“blow it the fuck out into space” is always a good strategy).

“Aliens”

Fox

And yet, even her most iconic moments, she stays human. Eventually tasked with leading the skeleton crew left behind after Dallas and John Hurt’s Kane bite it, her desire to live often results in moments of near hysteria. (Few people can screech “SHUT UP!” with the pure force that Weaver-as-Ripley can.) At one point, an orders-following android asshole tries to kill her with a periodical and a bad attitude, and the wild-eyed, sweat-covered Ripley that emerges from the encounter is as relatable an image as “Alien” can offer up.

She’s terrified, but she’s also the only person who can persevere in the face of seemingly insurmountable odds. It’s ugly and messy and scary as hell, but it works. Ripley survives.

Even before Ripley makes her grand stand in “Alien,” women loom large in Scott’s film — the Nostromo’s main operating system is called Mother, and Veronica Cartwright’s third-billed turn as Lambert is often overlooked for its potent emotionality — a theme that has thankfully continued throughout the series, with Weaver returning to kick even more ass in “Aliens,” “Alien 3,” and “Alien: Resurrection” (as a clone), where she was joined by Winona Ryder in another compelling female role. The latest arm of the franchise kicked off with “Prometheus,” which centers on Noomi Rapace’s ill-fated Elizabeth Shaw, and also boasts turns from Charlize Theron and Kate Dickie.

Katherine Waterston takes over lead duties in this week’s opener “Alien: Covenant,” likely kickstarting her own franchise (Scott has made it clear that he intends to continue the series). In December, Waterston was on hand at a special Fox event to show off an early look at the film, and she minced no words when it came to talking about the role that Ripley and Scott have played in delivering exciting female characters to the blockbuster space.

“People are talking a lot these days about the progress we’re making, or storytelling with great roles for women,” Waterston said during the event. “Maybe Ridley’s not getting enough credit. He’s been doing it for a very long time…I think his attitude about it is very similar to my own. It just seems obvious. There are a lot of cool, complicated women out there. It’s not rocket science.” (Waterston is joined in the film by a cadre of other cool actresses, including Amy Seimetz and Carmen Ejogo.)

Ripley’s fear is most palpable during her final face-off with her alien intruder — it’s hard to marry wide-eyed terror with the swagger to carry an actual flamethrower, but Weaver does it in style — and “Alien” concludes with its heroine proving victorious, while still knowing full well what she’s had to sacrifice to get there. That’s the true genius of Ripley, the full embodiment of a “strong female character” who also doesn’t shy away from the characteristics that keep her human and relatable.

She saves the world, saves herself, saves her cat, and still finds the time to craft one last log entry to tell the world what has transpired and what’s she done to keep the monsters at bay. Need to get a job done? Send Ripley. Send a woman.